A Reference Signal (RS) is a symbol used for Channel quality estimation and coherent demodulation in the downlink. To demodulate different downlink physical channels coherently, a User Equipment (UE) requires complex valued channel estimates for each subcarrier.
In the Long Term Evolution (LTE) radio access network, known reference symbols are inserted into a time-frequency resource grid. The reference signal is mapped to resource elements spread evenly in the resource grid, in an identical pattern in every resource block.
FIG. 1 is a diagram depicting time-frequency resource grids with typical Cell-specific Reference Signal (CRS) positions for one-antenna port and two-antenna port configurations. When transmitting with several antennas, each antenna must transmit a unique reference signal. When one antenna transmits its reference signal, the other antenna must be silent, as shown by the Xs in the reference symbol locations. The mapping of the reference signal on the resource grid therefore depends on the antenna configuration. The pattern of reference signals can be shifted in frequency compared to FIG. 1. Which one of the six possible frequency shifts to use depends on the Physical Cell Identity (PCI) sent on the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS).
In the conventional LTE System, the Cell Specific Reference Signal (CRS) power can be provisionally boosted by 3 dB when an RS Power Boost parameter is enabled by making use of the unused power available due to the corresponding silent resource element. The unused power of the silent resource element can be added to the reference signal resource element when the RS Power Boost parameter is enabled. This in turn leads to a 3 dBb boost of the Reference Signal Resource Element Power in comparison to the default value.
The existing method of CRS Power Boost by 3 dB or any other fixed value may unnecessarily increase the CRS footprint of the RS Power Boost-enabled Cell Site which could possibly degrade the radio network performance due to several reasons. First, the existing method may degrade the cell-edge performance of an overlapping cluster of cell sites by becoming a potential interferer due to the higher degree of overlap with its neighboring cell site clusters. Second, the existing method may increase the handover failure rate to same or legacy technologies. Third, the existing method may potentially reduce the average cell-site throughput and the connected user capacity if the power boost leads to covering unwanted far-off users operating in a lower order modulation and coding scheme (MCS) and in transmit diversity, i.e., Multiple Input Multiple Output (MIMO) schemes with a greater number of retransmissions than before. Fourth, the existing method may increase the Uplink (UL) Received Signal Strength Indicator (RSSI), i.e., the uplink noise and interference level which can potentially degrade the uplink throughput performance. Fifth, the existing method may increase the Random Access Channel (RACH) failure rate due to coverage imbalance between the UL and DL.